The present invention relates to novel 1,3-diaza-9-thia-anthracene-2,4-diones and to a photopolymerizable mixture which contains, as the essential components,
(a) a polymeric binder PA1 (b) a polymerizable compound having at least two terminal, ethylenically unsaturated groups and a boiling point of more than 100.degree. C., and PA1 (c) a 1,3-diaza-9-thia-anthracene-2,4-dione as the photoinitiator. PA1 (a) a polymeric binder PA1 (b) a polymerizable compound having at least two terminal, ethylenically unsaturated groups and a boiling point of more than 100.degree. C., and PA1 (c) a polynuclear N-heterocyclic compound as photoinitiator. PA1 R.sup.2 denotes an alkoxy, carboxyl or alkoxy-carbonyl group, or PA1 inhibitors to prevent thermal polymerization of the monomers, PA1 hydrogen donors, PA1 substances regulating the sensitomeric PA1 properties of layers of this type, PA1 dyes, PA1 colored and uncolored pigments, PA1 color formers, PA1 indicators, PA1 plasticizers, etc.
Photopolymerizable mixtures which contain the components (a) and (b) and a polynuclear heterocyclic compound as the photoinitiator are known.
In German Pat. No. 20 27 467 (equivalent to British Patent Specification No. 1,354,541) specific derivatives of acridine and phenazine are described as initiators.
German Pat. No. 20 39 861 (equivalent to U.S. Pat. No. 3,765,898) discloses similar mixtures containing quinoxaline derivatives or quinazoline derivatives as initiators.
All these compounds act as excellent initiators when they are irradiated with actinic light, particularly from light sources emitting in the near ultraviolet range. But in recent times, metal halide-doped gas discharge lamps have become more and more commonly used for copying purposes because of their high luminous efficiency, and since these lamps have stronger emission values in the border range of the visible light, i.e., at about 400 nm and higher, than the hitherto conventionally used light sources, such as, for example, mercury vapor lamps, the absorption values of the known highly efficient initiators are no longer optimally matched to the emissions of these light sources. Moreover, the variations possible by substitution of the known heterocyclic initiators are limited, i.e., by means of known production processes it is possible to modify other properties, such as solubility in aqueous or organic solvents or compatibility with various photopolymerizable mixtures, to only a limited degree by a purposeful synthesis.
In the Journal of Heterocyclic Chemistry 18, p. 1,329 (1981), 1,3-diaza-9-thia-anthracene-2,4-diones are described which in their 6-position are either unsubstituted or substituted by a chlorine atom or a methyl group. In the publication, these components are tested for their oxidation capacity with respect of alcohols. Other uses are not mentioned.